Target-state dependence of cross sections for reactions on statically deformed nuclei

Dietrich, Frank; Thompson, I. J.; Kawano, Toshihiko

doi:10.1103/physrevc.85.044611

Cited by 33 publications

(35 citation statements)

References 28 publications

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“…The largest difference is at most 0.7% seen in σ CN . Such a good agreement amongst different CC codes is also reported elsewhere [17]. Although we show the comparison at 100 keV only, in general the agreement is improved as the incident energy increases.…”

Section: Coupled-channels Optical Modelsupporting

confidence: 89%

Inter-comparison of Hauser-Feshbach model codes toward better actinide evaluations

et al. 2017

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Section: Coupled-channels Optical Modelsupporting

confidence: 89%

Inter-comparison of Hauser-Feshbach model codes toward better actinide evaluations

et al. 2017

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“…It was shown that the common practice of calculating neutron cross sections with three coupled levels in K = 0 + ground-state bands is inadequate [7]. This result was confirmed and generalized in a new comprehensive study by Dietrich et al [8], but none of these papers included additional vibrational bands in the coupling scheme of even-even nuclei or additional rotational bands in odd-A nuclei.…”

Section: Introductionmentioning

confidence: 93%

“…quantity for statistical reaction modeling. It has been shown that σ CN (E) strongly depends on employed coupled-channels couplings [8]. The proposed extension should account for multiple-band couplings, while keeping the achieved quality of description of the whole set of scattering data (e.g., total cross-section data above 5 MeV were described by the RIPL 2408 potential within the quoted experimental uncertainty of about 1.5%).…”

Section: Introductionmentioning

confidence: 99%

Nucleon scattering on actinides using a dispersive optical model with extended couplings

et al. 2016

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The Tamura coupling model [Rev. Mod. Phys. 37, 679 (1965)] has been extended to consider the coupling of additional low-lying rotational bands to the ground-state band. Rotational bands are built on vibrational bandheads (even-even targets) or single-particle bandheads (odd-A targets) including both axial and nonaxial deformations. These additional excitations are introduced as a perturbation to the underlying axially symmetric rigid-rotor structure of the ground-state rotational band. Coupling matrix elements of the generalized optical model are derived for extended multiband transitions in even-even and odd-A nuclei. Isospin symmetric formulation of the optical model is employed. A coupled-channels optical-model potential (OMP) containing a dispersive contribution is used to fit simultaneously all available optical experimental databases including neutron strength functions for nucleon scattering on 232 Th, 233,235,238 U, and 239 Pu nuclei. Quasielastic (p,n) scattering data on 232 Th and 238 U to the isobaric analog states of the target nucleus are also used to constrain the isovector part of the optical potential. Lane consistent OMP is derived for all actinides if corresponding multiband coupling schemes are defined. For even-even (odd-A) actinides almost all low-lying collective levels below 1 MeV (0.5 MeV) of excitation energy are coupled. OMP parameters show a smooth energy dependence and energy-independent geometry. A phenomenological optical-model potential that couples multiple bands in odd-A actinides is published for a first time. Calculations using the derived OMP potential reproduce measured total cross-section differences between several actinide pairs within experimental uncertainty for incident neutron energies from 50 keV up to 150 MeV. The importance of extended coupling is studied. Multiband coupling is stronger in even-even targets owing to the collective nature of the coupling; the impact of extended coupling on predicted compound-nucleus formation cross section reaches 5% below 3 MeV of incident neutron energy. Excitation of multiple bands in odd-A targets is weaker owing to the single-particle nature of the coupling. Coupling of ground-state rotational band levels in odd-A nuclei is sufficient for a good description of the compound-nucleus formation cross sections as long as the coupling is saturated (a minimum of seven coupled levels are typically needed).

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“…This was modeled using the ESGM level densities (with a 5% adjustment via the a-parameter), the Koning-Delaroche potential, and the MLO gamma strength function. Since the ground state deformation has a value of β 2 = 0.302, CC were invoked (a default number of four levels were coupled -the conclusions of [19] don't apply for charged particles subbarrier). Although [29] states that a CC approach gives enhancements in the transmission functions for both positive and negative Q-values subbarrier, probably due to the relatively small barrier a minimal overall improvement was observed in comparison to the absense of CC (graph of spherical case not shown).…”

Section: Se(pγ)mentioning

confidence: 99%

“…Seven collective levels were coupled following the prescription in ref. [19]. The parabolic representation of microscopically determined HFB fission barriers were used.…”

Section: Introductionmentioning

confidence: 99%

EMPIRE: A code for nuclear astrophysics

Palumbo

2013

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Abstract. The nuclear reaction code EMPIRE is presented as a useful tool for nuclear astrophysics. EMPIRE combines a variety of the reaction models with a comprehensive library of input parameters providing a diversity of options for the user. With exclusion of the directsemidirect capture all reaction mechanisms relevant to the nuclear astrophysics energy range of interest are implemented in the code. Comparison to experimental data show consistent agreement for all relevant channels. IntroductionFor the majority of elements heavier than iron, nucleosynthesis occurs mainly via neutron capture reactions in the r-and s-processes. The fission channel needs to be considered in the r-process for heavy nuclei (Z > 80) [1] in which fission barriers are low. Of particular importance are the superheavy elements (SHE) since they may determine the upper end of the nucleosynthesis flow [2] which may only be reached via certain nuclear physics inputs [3]. Although the calculated and measured fission cross sections globally differ by less than a factor of three [4], current extrapolations for r-process simulation models are still unreliable. The neutron spectrum typical of s-process sites can be described by a Maxwell-Boltzmann distribution (MBD). Neutron captures have their relevant energies around the maximum of the Maxwell-Boltzmann distribution (MBD), E o ≈ kT [5]. Stellar neutron capture cross sections in the mass region of the weak s-process are often not available with the required accuracy for abundance determination. The main mechanism of synthesis for the p-nuclei are photodisintegration reactions. A reprocessing of initial s-seed distribution [6] occurs via (γ,n) reactions with subsequent alpha (γ,α) or proton emission (γ,p) branchings. Simulation models have had problems reproducing the abundance distribution for the p-nuclei for Type II supernova [7]. The situation is ameliorated when considering Type 1a supernovae as a site of synthesis [8].The heavier nuclei are formed via reactions at a high enough level density such that the Hauser Feshbach (HF) formulation applies. EMPIRE [9] is a nuclear reaction model code that accepts nucleons, γ's, and several light ions (including α-particles and deuterons) in the incoming and outgoing channels. In the presence of direct reactions, the Engelbrecht-Weidenmüller transformation can be invoked to account for the interference between compound nucleus (CN) and direct. Resonance treatment (r-matrix formalism) is beyond the scope of the code and will therefore be ignored (neutron resonances [10] can be invoked from the resonance module). The bulk of the incoming flux is treated in terms of the HF formulation with the width fluctuation correction accounted for by the HRTW [11] model. The incident channel can be treated in terms

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Target-state dependence of cross sections for reactions on statically deformed nuclei

Cited by 33 publications

References 28 publications

Inter-comparison of Hauser-Feshbach model codes toward better actinide evaluations

Inter-comparison of Hauser-Feshbach model codes toward better actinide evaluations

Nucleon scattering on actinides using a dispersive optical model with extended couplings

EMPIRE: A code for nuclear astrophysics

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